When a person's kidney does not function properly uremia is developed. Dialysis is a well established treatment technique for uremia. Essentially, dialysis artificially replaces the functions of the kidney. There are two distinct types of dialysis; hemodialysis and peritoneal dialysis.
Hemodialysis involves withdrawing blood from the body and cleaning it in an extracorporeal blood circuit and then returning the cleansed blood to the body. The extracorporeal blood circuit includes a dialyzer which comprises a semipermeable membrane. The semipermeable membrane has a blood side and a dialysate side. Waste substances and excess fluid is removed from the blood (passing on the blood side of the semipermeable membrane) through the semipermeable membrane over to the dialysate side of the semipermeable membrane.
Hemodialysis may be performed in three different treatment modes; hemodialysis, hemofiltration, and hemodiafiltration. Common to all three treatment modes is that the patient is connected by a blood line to the dialysis machine, which continuously withdraws blood from the patient. The blood is then brought in contact with the blood side of the semipermeable membrane within the dialyzer in a flowing manner.
In hemodialysis, an aqueous solution called dialysis solution is brought in contact with the opposite membrane surface, the dialysate side, in a flowing manner. Waste substances (toxins) and solutes are removed/controlled mainly by diffusion. Excess fluid is removed by applying transmembrane pressure over the semipermeable membrane. Solutes and nutrients may diffuse in the opposite direction from the dialysis solution, through the semipermeable membrane and into the blood.
In hemofiltration, no dialysis solution is brought in contact with the dialysate side of the semipermeable membrane. Instead only a transmembrane pressure is applied over the semipermeable membrane thereby removing fluid and waste substance from the blood through the semipermeable membrane wall and into the dialysate side thereof (convective flow). Fluid and waste substances are then passed to drain. To replace some of the removed fluid, a correctly balanced electrolyte/buffer dialysis solution (also named infusion fluid or replacement fluid) is infused into the extracorporeal blood circuit. This infusion may be done either pre the dialyzer (pre-infusion mode) or post the dialyzer (post-infusion mode) or both.
Hemodiafiltration is a combination of hemodialysis and hemofiltration, a treatment mode that combines transport of waste substances and excess fluids through the semipermeable membrane wall by both diffusion and convection. Thus, here a dialysis solution is brought in contact with the dialysate side of the semipermeable membrane in a continuously flowing manner, and a dialysis solution (also named infusion fluid or replacement fluid) is used for infusion into the extracorporeal blood circuit in pre-infusion mode, post-infusion mode or both.
For many patients, hemodialysis is performed for 3-5 hours, three times per week. It is usually performed at a dialysis center, although home dialysis is also possible. When home dialysis is performed the patient is free to perform dialysis more frequently and also in more gentle treatments with longer duration, i.e. 4-8 hours per treatment and 5-7 treatments per week. The dose and treatment duration may be adjusted to each patient's demands and needs.
In the case of patients suffering from acute renal insufficiency, a continuous treatment, throughout a major portion of the entire day for up to several weeks, a continuous renal replacement therapy (CRRT), or intermittent renal replacement therapy (IRRT) is the indicated treatment depending on the patient's status. Also here the removal of waste substances and excess fluid from the patient is effected by any or a combination of the treatment modes hemodialysis, hemofiltration and hemodiafiltration.
In a peritoneal dialysis treatment a hypertonic dialysis solution is infused into the peritoneal cavity of the patient. In this treatment solutes and water is exchanged in the capillary vessels of a patient's peritoneal membrane with the hypertonic dialysis solution. The principle of this method is diffusion of solutes transferred according to the concentration gradient and water migration due to the osmotic differences over the peritoneal membrane.
The dialysis solutions used in all the above dialysis techniques contain mainly electrolytes like sodium, magnesium, calcium, potassium, an acid/base buffer system and optionally glucose or a glucose-like compound. All the components in dialysis solutions are selected to control the levels of electrolytes and the acid-base equilibrium within the blood and to remove waste materials from the blood.
Dialysis solutions are today prepared from different types of concentrates. It may be liquid concentrates of different degree of concentration, where the acid/electrolyte part is separated from the buffer part. It may be provided in highly concentrated volumes of 1-8 L in bags for bedside use, or in more diluted concentrated volumes of 5-20 L in canisters, which still are for bedside use. Concentrates may also be prepared in central tanks in volumes of 300-1000 L.
When using bicarbonate as a buffer component in the dialysis solution, bicarbonate is often provided as a dry concentrate for on-line-preparation of saturated bicarbonate containing concentrate. The saturated bicarbonate containing concentrate is thereafter mixed with an acid/electrolyte concentrate and further diluted with purified water to produce the on-line prepared dialysis solution.
Dialysis solutions have improved in quality over the years, and the availability of concentrated precursor compositions for further dilution and mixing with other components into a ready-for-use dialysis solution have decreased the costs and improved the environmental issues.
One way to further limit the costs and improve the environmental issues would be to provide a dialysis precursor composition in which all components are dry. However, having all components as dry components adds new problems.
Firstly, dry acid and bicarbonate powder are not compatible. When a small amount of humidity is present, bicarbonate will break down to carbon dioxide.
Secondly, magnesium chloride and calcium chloride mixed with bicarbonate will provide areas were the solubility product of calcium carbonate and/or magnesium carbonate will be exceeded, which would cause precipitation thereof when water is added during preparation of a concentrate or a dialysis solution.
Thirdly, even if bicarbonate is excluded to a separate cartridge, still problems would be experienced. E.g. caking and lump formation of the different components will render the dissolution thereof more difficult or even impossible when preparing the ready-for-use dialysis solution.
Fourthly, if glucose is present, a discoloration of the precursor, and later on, the ready-for-use dialysis solution would arise as a result of glucose degradation products, which should be avoided due to toxicity and limits set by authority regulations, e.g. European Pharmacopeia.
All the problems above are due to the presence of humidity within the dry precursor compositions.
In prior art this has been solved by preparing granulates of the different components and creating different layers of the different components within each granulate, like disclosed in EP0567452 or EP1714657.
However, this still may give rise to interactions between the different layers, and it is also a time-consuming matter of providing a completely and properly dissolved granulate for the preparation of the ready-for-use dialysis solution. Further, it is difficult to ensure proper composition and concentration of the different components both within the granulate and thus also within the finally prepared ready-for-use dialysis solution.